This application focuses on provision of booster programming in early emerging adulthood and extends the research on Project Towards No Drug Abuse (TND), a school-based drug abuse prevention program funded by the National Institute on Drug Abuse since 1992. This program is considered a model or exemplary program by numerous government agencies. The primary target population of our ongoing research is youth from the alternative school system (continuation high schools, CHSs) in California. While promising classroom program effects have been obtained in previous trials, only some effects have been maintained past a one-year follow-up (main effects on hard drug use and cigarette smoking, but not for marijuana use or alcohol use). A systematic test of booster programming seldom has been completed in drug abuse prevention research in general, and has never been conducted with Project TND. Further, current data indicate that drug use and abuse peak during late adolescence and emerging adulthood, yet few drug abuse prevention initiatives have been developed targeting late adolescence and emerging adulthood. Thus, to sustain and possibly enhance long-term outcomes of Project TND during the transition into early emerging adulthood, we propose to develop, implement, and test a carefully planned, multi-year, motivational-interview-based, telephone-delivered booster program following implementation of the TND curriculum in the CHS classroom. In a three condition experimental design, we will manipulate whether or not youth receive brief TND telephone boosters sessions in addition to the 12-session TND classroom curriculum. These two conditions (TND only or TND plus the booster component) will be compared to standard care. In this project, we examine if the addition of a booster component will provide an incremental effect on drug use behavior. We will also explore potential moderating and mediating relationships of Project TND and drug use outcomes. This application addresses prevention of drug abuse, a critical public health problem. We propose to test the efficacy of a booster intervention targeting alternative high school youth, who are at higher risk for development of drug abuse than are youth in regular high schools.